Magenta Ain't A Colour

A beam of white light is made up of all the colours in the spectrum. The range extends from red through to violet, with orange, yellow, green and blue in between. But there is one colour that is notable by its absence (click here to check). Pink (or magenta, to use its official name) simply isn’t there. But if pink isn’t in the light spectrum, how come we can see it?

Here’s an experiment you can try: stare at the pink circle below for about one minute, then look over at the blank white space next to the image. What do you see? You should see an afterimage. What colour is it? Link